EXPLAINER: How Exit Polls Work

ABC News will conduct exit polls in all 50 states on Election Day, along with polling partners CBS, CNN, Fox, NBC and The Associated Press. These news organizations comprise the National Election Pool, which contracted with Edison Media Research/Mitofsky International to run the exit polls. The data gathered in these polls provide the best source of information about who voted, for whom they voted and why.

Here are answers to some frequently asked questions about exit polls:

What are exit polls?

Reaching voters at that moment is important because it overcomes the problem pollsters have conducting election polls by telephone: People sometimes misreport whether they voted or not. The "who won and why did they win" reporting on election night is gleaned mainly from exit poll results, with the information reaching most Americans by television, and increasingly through the Internet.

How are exit polls conducted?

Interviewers stand outside polling places in precincts that are randomly selected in each state. They attempt to interview voters leaving the polling places at specific intervals (every fourth or 10th voter, for example).

Voters who agree to participate in the poll fill out a paper questionnaire and place it in a ballot box. Interviewers phone in results three times during the day. When a voter refuses to participate, the interviewer notes the gender and approximate age and race of that voter. In this way, the exit poll can be statistically corrected to make sure all voters are fairly represented in the final results.

What sorts of questions are asked in an exit poll?

The typical exit poll questionnaire asks questions of voters that measure the following:

who they just voted for in key races

what opinions they hold about the candidates and important issues

their demographic characteristics

Here's an example of an exit poll issue question from the 2008 Democratic primary in New Hampshire:

Which one of these three issues is the most important facing the country?

Are exit polls accurate?

Exit polls, like any other survey, are subject to sampling errors. Before news organizations report any exit poll results or make projections, therefore, they compare results to pre-election polls, past precinct voting history, and have statisticians and political experts carefully review the data. After the polls close, the exit poll results are weighted using the actual vote count to make the data more accurate. Projections are never based solely on the results of exit polls.

How do exit polls account for the people who vote by mail?

In the last national election, nearly 22 percent of Americans voted before Election Day, using some form of absentee or early voting. Some experts believe a third of the country's voters may vote earlier than Election Day in 2008. Capturing information about these voters is challenging, but it is critical to report accurate information about all voters on Election Day. In states with high numbers of absentee/early voters, telephone polls are conducted to reach those voters. Data from these telephone polls are combined with the exit poll data to provide a complete portrait of all voters.

When will exit poll results be reported?

On Election Day, there is a strict quarantine on any news coming from the early waves of exit poll data until 5 p.m. ET. By about 5:45 p.m., some initial demographic information about voter turnout will be available on ABCNews.com. However, no winners will be projected until polls are closed, so announcements come state-by-state as individual state polls close. Information will be updated continually throughout the evening on ABCNews.com and on all ABC News programs.